Bridge slabs retrofitting with concrete overlay: Codes comparison and parametric design

The damage caused to reinforced concrete slabs by weathering or use of deicing salts, as well as the increase of traffic loads in terms of frequency and intensity often leads to the necessity of retrofitting bridge slabs with partial water-jet demolition of the upper part of the original slab and the casting of a new layer of concrete on top. To guarantee a monolithic behavior after the retrofitting intervention, a proper connection system between the old and new concrete layers should be designed. The efficiency of the retrofitting of bridge slabs with concrete overlay connected through post-installed rebars is influenced by phenomena such us adhesion, friction, and dowel action of the connectors, as well as the type of loading. In this paper, the approaches proposed by different Codes for the evaluation of the shear resistance of the old-to-new concrete interface are critically reviewed, discussing the main differences and design parameters affecting the results. The different formulations are then applied to two case studies of concrete bridge decks retrofitted with concrete overlay. Finally, to propose better design configurations, some parametric analyses are performed to analyze the influence of certain parameters on the interface resistance. The more comprehensive formulation is given by EOTA TR066, which considers the actual stress in the steel connector. However, in case of thick overlay and sufficient embedment depth of the connector, Model Code 2010 seems to be the most conservative and complete approach. The parametric analysis highlighted that concrete strength and reinforcement ratio have a high influence on the shear resistance of the interface. However, the concrete strength is not a real design parameter since the original material of the bridge slab cannot be changed.